1. Reproductive function in all vertebrates is regulated by hypothalamic secretion of the gonadotropin-releasing hormone (GnRH), a decapeptide, via the pituitary-gonadal axis. GnRH action is mediated through a class A rhodopsin-like 7-transmembrane G protein- coupled receptor. GnRH has been the subject of intense research since the 1970s due to its significance for understanding reproductive biology and for developing medical therapies. In light of the crucial role GnRH plays in human physiology and disease, its receptor also has been an important area of research interest. There is considerable interest in understanding the function of each residue in the GnRH peptide to facilitate the design of analogs with maximum efficiency as agonists or antagonists to the GnRH receptor for use as pharmaceutical agents. However, it is challenging to determine how an altered residue may affect the binding of the analog or its ability to activate the receptor. Furthermore, the change of a single residue could alter the structure of the peptide thereby changing the three dimensional orientation of functional groups from other residues that are involved in receptor interaction The lamprey genome offers a model system in which novel receptors can be identified from where they are annotated as to their sequence and their percent identity. Receptors of interest can be cloned, expressed and tested for function. We have identified from our recent studies a unique lamprey GnRH receptor which shares several characteristics of both type I and type II vertebrate GnRH receptors which suggests that this receptor has retained ancestral characteristics that can provide insight into the function and evolution of the GnRH receptor family. We propose to perform a series of site-directed mutagenic studies and then examine the expressed receptors for ligand binding, inositol response, cAMP accumulation which may determine, in part, the key residues involved in signaling and regulation of the GnRH receptor. Our specific aims are 1) to characterize the key functional features of the lamprey GnRH receptor-I by site-directed mutagenic studies and 2) to identify novel form(s) of GnRH receptors in lamprey by screening the lamprey genome, followed by cDNA cloning and functional studies. Studying the lamprey genome is a touchstone for understanding genes that arose in the vertebrates and offers an innovative approach to therapeutic research. Project Narrative: The lamprey genome offers a model system in which novel hormones and receptors involved in reproduction can be identified. Receptors of interest can be cloned, expressed and tested for function leading to the proposed new ligand molecules to be tested for therapeutics/ oncology. Studying the lamprey genome is a touchstone for understanding genes that arose in the vertebrates and offers an innovative approach to therapeutic research. [unreadable] [unreadable] [unreadable]